A healthy person acquires infection when a female Anopheles mosquito, containing infective stages of parasite (sporozoites) in its salivary glands, bites him for sucking his blood. The mosquito punctures the host's skin by its proboscis and first introduces some saliva into blood stream. Along with saliva, thousands of sporozoites contained therein are also inoculated. Sporozoites represent the infective forms of parasite. These are small spindle-shaped, slightly curved or sickleshaped, and uninucleate organisms, measuring ll-12(im in length and 0.5-1 pm in width. After infection sporozoites enter liver cells here after a few divisions, micrometacryptomerozoites are formed that enter RBC's and gametocytes are formed here in RBC's.